Since the beginning of the twentieth century inventors have proposed many solutions to vary the compression ratio of internal combustion engines. Almost all of them were found to be ineffective, impractical or too complicated to be used except in limited production in areas outside the usual commercial engine markets where higher initial cost and costly maintenance were considered acceptable.
In internal combustion engines as usually constructed the clearance volume is fixed. The pressure to which the air in the combustion chamber can be compressed is limited by practical considerations. In order that the power cylinder may receive larger quantities of air without exceeding the permissible pressure means must be provided for increasing the clearance volume when required.
It has been demonstrated that compression-ignition engines require peak pressure control devices that are completely automatic if better power-to-weight ratios as well as substantial improvements in cold starting ability and potential for multi-fuel operation and greater economy in production is to be obtained.
In spark-ignition engines it is apparent that a practical variable compression ratio device would also permit a significant improvement in part load fuel consumption without reducing the maximum output potential and eliminates the harmful effects of detonation and permit the use of fuels with lower octane ratings.
As the current trend to pressure charge engines continues it becomes evident that future internal combustion engines will require some type of automatic peak pressure control device if higher power-to-weight ratios and improved fuel economies are to be achieved.